Gromit,
Yes indeed... any business can impose Terms and Conditions.. except where those terms and conditions breach regulations, international treaties or the law. For international travel, these are governed by treaty and no airline can create T&C's which abrogate that treaty. Therefore on international travel, the airline cannot exclude electrical items. This doesn't seem to stop them trying. Equally, for domestic travel, the airlines are regulated (with a light touch, sadly) by the DOT. Despite their best efforts, airlines cannot change the regulations by putting it in their T&C's. This explains why many airlines have been heavily fined by the DOT when they are found to be in breach. I have provided a link to a fine for Spirit in an earlier posting, in which one of the breaches was specifically an attempt by Spirit to refuse to cover the theft of a laptop.

So, I am afraid you are wrong. You can impose Terms and Conditions, except where they breach the law.